In traditional lift systems with a lift car, the lift car is led across a traction means, such as at least one traction cable or at least one traction belt, which is led across a driving sheave and deflection rollers and connected to a counterweight. Lift car and counterweight can travel along respective guides in a lift shaft. The lift car is typically configured with guide rollers, which interact with the lift car guide (guide rails). Furthermore, a travelling cable is connected to the lift car. By means of this travelling cable, the lift car is supplied with electric energy, for example. Moreover, data can be exchanged via the travelling cable between the lift car and an external computer or control unit.
The travelling cable is typically secured at one end to one side or the floor of the lift car, and at the other end to or in the lift shaft. Especially for fastening of the travelling cable to a side wall of the lift car (which is preferable for certain designs of a lift system), unequal loading of the lift car occurs on account of the weight force of the travelling cable, especially on the guide rollers.
In order to ensure good riding qualities and good riding comfort, the lift car must be balanced as precisely as possible. Therefore, a balancing weight is provided on the lift car to compensate for this variable loading due to the travelling cable along the length of the shaft. In this way, it is possible to compensate a moment or torque exerted by the travelling cable due to its weight force on the guide rollers of the lift car, so that the loading of the guide rollers can be lessened.
However, such a compensation by means of a balancing weight is only optimal in a particular position of the lift car in the lift shaft, usually the middle of the lift shaft. In the other positions there is still a more or less unequal distribution of forces on the guide rollers. In particular in the uppermost and lowermost position of the lift car in the lift shaft, the greatest loading of the guide rollers occurs.
It is therefore desirable to provide a way to effectively and easily minimize the loads exerted by a travelling cable of a lift car on the lift car or its guide rollers.